I can't comment on how it will look, that's a bit objective and it all depends on what else you plant on putting in there for the aquascape...although I have seen some sandy "beaches" and sand "paths" in tanks and they looked pretty neat.
I love dirt tanks, both of mine are. Careful where you get your topsoil though. If you decide on store bought use Miracle Grow Organic. Also, at one point you said a thin layer of sand on part of the tank...and that's fine, just keep in mind your going to want at least and inch of whatever on your topsoil to prevent accidental top soil explosions, lol.